Analysis and design of a microstrip reflectarray using patches of variable size

In a great number of microwave applications a highly directive antenna with a main beam scanned to a certain angle is required. To achieve this a certain aperture illumination with progressive phasing is used. The two primary ways to do this are reflectors and arrays. The reflector antenna uses its geometry to create the desired phase across the aperture, while the array employs distinct elements fed with progressive phasing. Reflector antennas are advantageous in the fact that they typically exhibit large bandwidth and low loss. The main disadvantage of the reflector is the geometrical constraint it imposes on the design. The most popular reflector, the parabolic reflector, also exhibits inherently high cross polarization levels. Microstrip patch arrays are lightweight, low-profile antennas that are capable of low cross polarization levels but typically have small bandwidth and fairly large loss at microwave frequencies. The more attractive features of reflectors and arrays are combined in the reflectarray. The steps taken in the design of a microstrip reflectarray using patches of variable size are outlined. Measured and theoretical results are shown for the finished design, and several important performance criteria are compared with the microstrip reflectarray.